Image:
Mouth of a Sevenspot Archerfish

Notes

Archerfishes have adaptations to the mouth which enable them to accurately spit a jet of water to knock insects out of overhanging branches. A deep groove runs along the roof of the mouth. A ridge along the top of the tongue fits into this groove. When an Archerfish shoots a jet of water, it raises its tongue against the roof of the mouth forming a tube. The gill covers are then quickly closed, which forces water along the tube. The tip of the tongue acts as a valve.